Windows Update can be very frustrating, especially when it fails after 10 hours!
There is a wonderful free tool to fix this problem, and also to perform many other free Windows maintenance tasks. It is called Reset Windows Update Tool.
Option 2 fixes most Windows Update issues, but if your system is really screwed up, try options 5, 6, 7 as well.
This tool must be run as Administrator. This proved to be more difficult than usual. I made a desktop shortcut to C:\Program Files"\wureset\wureset.exe Rut it did not run when I right-clicked and selected 'Run as Administrator'. When I went to the above location, and right-clicked on wureset.exe, there was no such option. (But I just tried it again after a reboot, and the admin option worked.) I eventually opened a commend window (as Administrator) and ran wureset from there. There are many ways to do thinks.